Hatchling vocalizations and beneficial social interactions in subterranean nests of a widespread reptile.

Signals are fundamental to communication, and theory suggests signals may evolve to coordinate cooperation on complex tasks. Several recent studies have demonstrated that hatchling turtles vocalize within the subterranean nest cavity, and these vocalizations are hypothesized to promote hatching synchrony and coordinate emergence from subterranean nests (social facilitation hypothesis). Here we test assumptions and predictions of the social facilitation hypothesis in the snapping turtle, Chelydra serpentina , a species with a broad distribution. First, we demonstrate that C. serpentina hatchlings have a vocal repertoire: we identified six types of vocalizations in a simulated nest environment, with one vocalization type occurring before egg pipping and all six types occurring in the 24 h following egg pipping and hatching. We found that Simpson's diversity was greater for vocalizations during the hatching stage compared to the emergence stage and was minimal during the prepipping stage. Second, we manipulated egg burial depth (shallow or deep) and sociality (presence or absence of siblings) in a 2 × 2 factorial design. We found that eggs in the social treatment hatched earlier and lost less mass while emerging from the nest, underlining a likely energetic benefit to hatchlings emerging with siblings versus emerging alone. Third, we tested a subhypothesis of the social facilitation hypothesis, which is that embryos cue hatching in response to hatchling vocalizations. However, vocalization playback to late-stage (prepipping) embryos did not alter pipping date relative to controls. Our combined results provide some support for the social facilitation hypothesis: there are likely energetic benefits to group emergence, embryos in a group hatch earlier, but earlier group hatching is not cued by vocalizations per se. Our study contributes to a growing literature on the adaptive significance of sociality in reptiles and helps disentangle the proximate drivers of vocalizations in hatchling turtles. • Snapping turtle hatchlings produce at least six vocalization types in the nest. • Relatively complex vocalizations were only present during hatching and emergence. • Eggs in the presence of clutchmates hatched earlier than eggs hatching alone. • Hatchlings emerging in a group lost less mass than hatchlings emerging alone. • Playback of pipping vocalizations did not cue hatching. [ABSTRACT FROM AUTHOR]